1. Field of the Invention
The present invention relates to an electric actuator, namely, an actuator to be operated by an electric motor adapted for opening and closing a damper of an air conditioner of a vehicle, and more particularly, to an electric actuator which can be easily constructed by combining a motor, a reduction gear unit which transmits the output of the motor to an output shaft adapted for opening or closing the damper, and a position-detecting unit which detect the position of the output shaft so as to control the motor.
2. Description of Related Art
An actuator for controlling the position of a damper provided with an air conditioner for use in a vehicle is proposed. As shown in FIG. 1 an air conditioner includes an air-refreshing (R/F) damper 1, an air-mixing (A/M) damper 2, and an exit change-over (MODE) damper 3. The actuator is provided with a reduction gear mechanism which transmits the rotation of a D.C. motor to an output shaft through which the air-refreshing (R/F) damper 1, the air-mixing (A/M) damper 2, and the exit change-over (MODE) damper 3 are opened or closed. The actuator is further provided with a position-detecting mechanism which includes brushes mounted on the output shaft and a plate carrying switching patterns connected to switches for an air-refreshing (R/F), an air-mixing (A/M), and an exit change-over (MODE) disposed at positions at which the switching patterns and the brushes contact with each other. The above-described mechanism detects the rotation angle of the output shaft so as to control the rotation of the motor. Referring to FIG. 1, the air conditioner includes a blower 4, an evaporator 5, and a heater core 6.
In the above-described known actuator, the reduction gear mechanism comprises a helical gear engaging with a worm gear fixed to the shaft extending from the motor and spur gears disposed between the output shaft and the helical gear. When a gear ratio is changed in this reduction gear mechanism, it is necessary to change the positions of all the spur gears and the gear-supporting shaft. Further, the number of reduction gears is required to change according to reduction gear ratios. It is necessary to change a reduction gear ratio according to a selected switching pattern of the switching patterns for the air-refreshing (R/F), the air-mixing (A/M), and the exit change-over (MODE). This increases the number of works and processes (position-changes of gears and gear-supporting shaft) for constructing the actuator. Furthermore, an erroneous gear may be mounted on the reduction gear mechanism because reduction gear ratios are required to be changed according to switching patterns. Moreover, it is difficult to automatically assemble gears, so that labor-saving cannot be accomplished. This causes the cost for manufacturing an air conditioner to increase. In addition, an air conditioner is required to be accurate in detecting the position of the output shaft and compact. However, a compact air conditioner causes the position-detecting section to be compact, which makes it difficult to mount brushes on the gear fixed to the output shaft and also correctly position the brushes and the plate on which the switching patterns are mounted. It depends on a correct positioning of the brushes and the plate carrying the switching patterns whether or not the damper stops with a high accuracy.